Tomatoes have recently received attention as a healthful food, particularly in view of the carotenoids which they contain. Popular sources of tomatoes in the diet are spaghetti and other red pasta sauces. Many consumers prefer tomato sauces which are freshly prepared because of improved taste. However, a difficulty encountered in the commercial preparation of fresh sauces is that breaking or cutting of tomatoes, eg, during dicing or crushing, especially breaking or cutting the tomato skins, causes the release of enzymes which can result in a rapid and usually undesirable decrease in the viscosity of the product. Consequently, heating to elevated temperatures is used to deactivate these enzymes, with the resulting loss of taste found in processed, as opposed to fresh packed, sauces.
Using fresh tomato products in preparing a tomato sauce (particularly calcium-treated raw diced tomatoes) can result in the sauce gelling. This is a result of the pectin and pectin-related enzymes not being deactivated in the raw tomatoes by heat. Pectin exudes from the raw tomatoes and combines with the available calcium to form a calcium pectate gel. It is usual in the practice of making a spaghetti sauce to use canned or aseptically processed diced tomatoes. The heat processing of the diced tomatoes inactivates the pectin enzymes and sets the pectin in the diced tomatoes. But again, heat processing generally has an impact on taste.
Generally, the best diced tomatoes are made using calcium chloride to firm the dices prior to processing. The calcium treated diced tomatoes can be a source of calcium for the gelling formation, although most tomato products contain enough calcium for gel formation to occur even without an additional source of calcium. The source of pectin is the unprocessed diced tomatoes. Pectin can also come from any fresh puree used in making the sauce although the main source of the excess pectin related to the gel has been identified as coming from the raw diced tomatoes.
Two enzymes which have been implicated in the above are pectin methyl esterase, which catalyzes cleavage of methoxy groups from pectin, and pectinase (also known as polygalacturonase or PG) which catalyzes depolymerization of the cleaved pectin molecules, which causes the reduction in viscosity. It is the demethoxylated pectins which are most suseptible to forming gels by combining with calcium ions.
Pectinase is sometimes used to degrade soluble and insoluble pectins with varying degrees of esterification for viscosity reduction, clarification, and depectinization and maceration of plant tissue in the production of fruit and vegetable juices. It is known that pectin will be deactivated by depolymerization by a small amount of pectinase.
It is documented that raw garlic and onion will under specified process conditions cause a tomato product (i.e., a sauce) to gel. U.S. Pat. No. 4,547,375, to Mersfelder et al. addresses how to prevent these gels and/or use these types of gels to thicken tomato based products. Mersfelder et al. disclose using the gelation mechanism provided by releasing methyl pectin esterase from onion and garlic to demethoxylate the pectin available in the tomato based product to generate a supply of low methoxyl pectin to increase the viscosity of the sauce. They also disclose that in sauces wherein the tomatoes were initially heat treated to inactivate the enzymes, gelling can be prevented by, e.g., a) heating the onion or garlic prior to their addition to the sauce or b) the addition of pectinase. Crandal et al. U.S. Pat. No. 5,206,047 recognized that high rapid heat treatment of pectin-containing juices will prevent gelling. Crandal et al. were confronted with the fact that the product they wanted to make could not tolerate a high heat manufacturing process without losing its product benefit. Their solution was to subject their product to high shear to destroy or prevent the gel. Unfortunately, high shear tends to destroy the appearance of distinct diced tomatoes in a sauce. Moreover, to subject a fresh pack tomato based sauce to sufficient heat in a short enough time to prevent some of the gelation would produce a product that lacked the flavor and texture benefits derived from making the product at lower temperatures, but results in the product having an undesirable texture because of the gel.